The present invention relates to electromechanical valves actuators and, more particularly, to compact electromechanical valve actuator assemblies and the arrangement of electromechanical valve actuators on an engine.
As engine technology advances and manufacturers strive to increase engine power, improve fuel economy, decrease emissions, and provide more control over engines, manufacturers are developing electromechanical valve actuators (also known as electromagnetic valve actuators or EMVA) to replace cam shafts for opening and closing engine valves. Electromechanical valve actuators allow selective opening and closing of the valves in response to various engine conditions.
Electromechanical valve actuators generally include two electromagnets and a spring loaded armature plate disposed between the electromagnets. The armature plate is movable between the electromagnets as the power coils are selectively energized to create a magnetic force to attract the armature plate to the energized electromagnet. The surface of the electromagnets to which the armature is attracted is generally referred to as a pole face, and the armature is operationally coupled to the valve so that as the armature moves between pole faces in a pole-face-to-pole-face operation, the valve is opened and closed.
Electromechanical valve actuators are generally formed as linear electromechanical valve actuators or lever electromechanical valve actuators. One problem with linear electromechanical valve actuators is that each linear electromechanical valve actuator operationally coupled to the associated valve includes a relatively large set of electromagnets for opening and closing the valves (FIG. 1). The size of the electromagnets makes it difficult to position all of the linear electromechanical valve actuators over a particular cylinder, especially for engines that have four or more valves per cylinder. The size of linear electromechanical valve actuators may also limit the ease of serviceability of the engine, such as restricting the space available for changing the spark plug. Another problem with linear electromechanical valve actuators is that linear electromechanical valve actuators generally have a substantial height extending from the cylinder head of an engine. The height of the linear electromechanical valve actuators creates difficulty in packaging the linear actuators on engines in today's compact engines and in today's full engine compartments. For example, linear electromechanical valve actuators may interfere with other engine parts, other components or accessories located in the engine compartment, and even the vehicle body, such as, the hood. Yet another problem with linear electromechanical valve actuators is that they generally draw a substantial amount of power from the vehicle's electrical system, as compared with lever electromechanical valve actuators, thereby putting additional demand on the alternator in today's power hungry vehicles.
In view of the drawbacks associated with linear electromechanical valve actuators, many manufacturers have recently turned to lever electromechanical valve actuators, which, due to their mechanical and magnetic properties, generally have substantial power savings over linear electromechanical valve actuators. Lever electromechanical valve actuators also generally do not protrude as far from the cylinder head as linear electromechanical valve actuators. However, a major problem with lever electromechanical valve actuators is still the package size required on the cylinder head. Due to the set locations of valves and spark plugs by engine designers, designs for lever electromechanical valve actuator assemblies on the engine have been traditionally limited. Most lever electromechanical valve actuators packaged on the cylinder head are arranged longitudinally in line with the elongated longitudinal cylindrical head extent of the cylinder head, as shown in FIG. 2. Therefore, each actuator group within the actuator assembly, and associated with a particular cylinder, is arranged laterally across the cylinder head with each individual actuator being arranged longitudinally with the cylinder head. More specifically, the pivot axes of each actuator aligned with the cylinder head longitudinal extent. As shown in FIG. 2, the lever electromechanical valve actuators on an engine having four valves 20 per cylinder 16 require significantly more space across a cylinder head than camshafts, thereby presenting packaging concerns in engine compartments where space is limited. Also, the arrangement of lever electromechanical valve actuators shown in FIG. 2 raises additional serviceability concerns, especially for the ease of servicing and replacing the spark plugs and in some arrangements, the space available for fuel injectors. The difficulty in changing the spark plug as well as servicing the actuators is compounded in that at least two of the actuators are completely within the perimeter of the cylinder walls extended toward the actuators. Therefore, there is a need for additional electromechanical valve actuator arrangements that minimize package space, provide ease of serviceability, and provide room for wiring assemblies and control modules communicating with the individual actuators.